The communication system that is a successor to the W-CDMA system and HSDPA system i.e. the LTE (Long Term Evolution) system has been studied by 3GPP that is the standardization group of W-CDMA, and the specification development work has proceeded.
In the LTE system, as a radio access scheme, OFDMA is used in downlink, and SC-FDMA (Single-Carrier Frequency Division Multiple Access) is used in uplink (for example, see Non-patent Document 1).
OFDMA is a system for dividing a frequency band into a plurality of narrow frequency bands (subcarriers), and allocating data onto each frequency band to perform transmission, actualizes high-speed transmission by densely arranging subcarriers in the frequency domain without interfering with one another even with part thereof overlapping, and is capable of enhancing spectral efficiency.
SC-FDMA is a transmission system for dividing the frequency band so that a plurality of terminals uses different frequency bands to perform transmission, and thereby enabling interference among the terminals to be reduced. SC-FDMA has the feature that the variation in the transmission power is decreased, and therefore, actualizes low power consumption in the terminal and wide coverage.
The LTE system is a system in which a plurality of mobile stations shares one, or two or more physical channels to perform communications both in uplink and downlink.
The channel shared by a plurality of mobile stations is generally referred to as the shared channel, and in the LTE system, is the “Physical Uplink Shared Channel (PUSCH)” in uplink, while being the “Physical Downlink Shared Channel (PDSCH)” in downlink.
Further, as a transport channel, the shared channels are the “Uplink Shared Channel (UL-SCH)” in uplink, and the “Downlink Shared Channel (DL-SCH)” in downlink.
Then, in the communication system using the above-mentioned shared channels, it is necessary to select a mobile station UE to assign a shared channel for each sub-frame (1 ms in the LTE system), and perform signaling to notify the selected mobile station UE of the assignment of the shared channel. In addition, the sub-frame may be also referred to as a TTI (Transmission Time Interval).
The control channel used for this signaling is referred to as the “Physical Downlink Control Channel (PDCCH)” or “Downlink L1/L2 Control Channel (DL L1/L2 Control Channel)” in the LTE system.
In addition, the processing for selecting a mobile station UE to assign a shared channel for each sub-frame is generally referred to as “scheduling”. In this case, a mobile station UE to assign the shared channel is dynamically selected for each sub-frame, and the processing may be referred to as “dynamic scheduling”. Further, “assign a shared channel” may be expressed by “allocate radio resources for the shared channel”.
For example, the information of the Physical Downlink Control Channel includes “downlink scheduling information”, “uplink scheduling grant”, etc. (for example, see Non-patent Document 2).
For example, the “downlink scheduling information” includes the allocation information of downlink resource block, ID of the UE, the number of streams, information on the precoding vector, data size, modulation scheme, information on HARQ (hybrid automatic repeat request), etc concerning the shared channel in downlink. In addition, the downlink scheduling information may be also referred to as downlink scheduling grant or downlink assignment information.
Further, for example, the “uplink scheduling grant” includes assignment information of uplink resource block, ID of the UE, data size, modulation scheme, transmission power information in uplink, information of demodulation reference signal in uplink MIMO, etc concerning the shared channel in uplink.
In addition, the above-mentioned “downlink scheduling information” and “uplink scheduling grant” may be collectively referred to as “downlink control information (DCI)”.
Meanwhile, in semi persistent scheduling (SPS) studied to actualize VoIP, etc., with respect to the downlink, it is configured that a radio base station eNB assigns downlink radio resources (PDSCH) to a mobile station UE in a fixed manner at predetermined intervals, starting at a sub-frame (assignment start time), as a starting point, in which the downlink scheduling information is transmitted to the mobile station UE via the PDCCH. Further, with respect to the uplink, the radio base station (eNB) assigns uplink radio resources (PUSCH) to a user equipment in a fixed manner at predetermined intervals, starting at a sub-frame (assignment start time), as a starting point, transmitted 4 ms after a sub-fame in which the uplink scheduling grant is transmitted to the user equipment via the PDCCH.
Further, in uplink of the LTE system, radio resources are assigned to each user equipment for a control signal of downlink radio quality information, scheduling request, etc. The downlink radio quality information is referred to as the channel quality indicator (CQI), and based on the CQI, the base station apparatus performs the above-mentioned dynamic scheduling and semi persistent scheduling. The scheduling request is a signal for the user equipment to request the base station apparatus to assign uplink radio resources. Further, in addition to the above-mentioned control signal, radio resources for a sounding reference signal may be allocated to each user equipment. Herein, the sounding reference signal is a reference signal (or a pilot signal) used in uplink scheduling and transmission power control, for example.
The control signal of the CQI, scheduling request and the like is transmitted with the PUCCH (Physical Uplink Control Channel) in a sub-frame in which the Uplink Shared Channel (UL-SCH) is not transmitted. Meanwhile, the control signal of the CQI, scheduling request and the like is multiplexed onto the Uplink Shared Channel (UL-SCH) and transmitted in a sub-frame in which the Uplink Shared Channel (UL-SCH) is transmitted.
In addition, in LTE, discontinuous reception (DRX) control is applied. The discontinuous reception control is applied in the case that the base station apparatus and the user equipment are connected with each other and that data to communication does not exit, and the user equipment in the discontinuous reception state receives the Physical Downlink Control Channel (PDCCH) periodically i.e. intermittently. In this case, it is essential only that the user equipment receives the Physical Downlink Control Channel (PDCCH) intermittently instead of all the timing, and it is thereby possible to reduce power consumption in the battery (battery saving). The time duration to intermittently receive the Physical Downlink Control Channel (PDCCH) in the above-mentioned discontinuous reception control is referred to as ON duration of DRX or On-duration. Further, a cycle to set the On-duration is referred to as the DRX cycle.
In addition, in order to enhance the effect of the above-mentioned battery saving, the above-mentioned control signal of the CQI, scheduling request, etc. is only transmitted during the On-duration when the discontinuous reception control is performed.
FIG. 12 shows an image diagram of SPS and DRX control. In the figure, the DRX cycle and the transmission interval of SPS are 20 ms, and the length of On-duration is 7 ms. With respect to DRX control, sub-frames with sub-frame numbers of “n×20˜n×20+6 (in addition, n is an integer)” are set for On-duration. Further, in SPS, the uplink scheduling grant for SPS is transmitted in sub-frame number 4 from the base station apparatus to the user equipment, and uplink radio resources (PUSCH) are allocated in a fixed manner to the user equipment at 20 ms-intervals starting from sub-frame number 8 four sub-frames after the sub-frame of sub-frame number 4.